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Old 04-28-2009, 10:47 PM   #1
mekrew
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High Velocity Porting

So I decided to go over to SMJ and post up asking what are some ways i can get a bit more grunt and top end out of my motard w/o doing crazy stuff like bore kits and some other things and make the motor less reliable but more power

one guy suggested bumping the compression with a bigger piston and some head work ...

but then there was "High Velocity Porting"
Here is the link I was directed to and it looks like a simple trick todo (minus taking the head off) for some more top end hp

http://www.mototuneusa.com/think_fast.htm
http://www.mototuneusa.com/homework.htm

thoughts ?

not saying im going todo it just wanted to know thoughts on this. not sure how much a difference 5hp on the top end makes

discuss...

blue = stock
green = 20% smaller
red = 30% smaller
R6PortingDynoSheet
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Old 04-28-2009, 10:59 PM   #2
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The stocker 450 KTM SMR makes right at 50 rwhp, plus or minus a pony. Adding 5 horses is a pretty significant amount. I have some doubts that a 10% power increase can come from hi-flow porting and nothing more in a single. But, that said, fundamentally, getting an internal combustion engine to take in, burn, and expel fuel/air, and do it quickly, is the key to power. This concept is called "volumetric efficiency", and it's a universal truth.

http://en.wikipedia.org/wiki/Volumetric_efficiency
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Old 04-28-2009, 11:08 PM   #3
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cool let me read up on that stuff ... i learn new stuff every day
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Old 04-28-2009, 11:10 PM   #4
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5 hp available from 7500 rpm on a little 450 is a pretty big deal.
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Old 04-28-2009, 11:18 PM   #5
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lets just say i was "thinking" about doing this ...

how much pocket damage might i expect ?
and would it be worth the pocket damage ?
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Old 04-28-2009, 11:23 PM   #6
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you should look into Low Velocity Porting
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Old 04-28-2009, 11:34 PM   #7
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That dyno graph is interesting.
Is this a stock head that had the ports modified to be smaller, or a ported head that was modified to be smaller?
Head porting is a art. If the ports are too small, they will restrict the flow of the intake/exhaust charge in and out of the combustion chamber.
If they are too big, you will loose inake/exhaust velocity that aids in skavenging. Ideally, you want the intake charge to hit the back of the intake valve with as much speed as possible as to force it's self into the chamber once opened. Same goes for the exhaust. You want it to leave the chamber as fast as possible. The exhaust gas has mass and the faster it moves, the more negative pressure it will carry behind it to aid in sucking out the exhaust gas on the next cycle.
I would consult a experienced KTM builder before jacking around with the head.
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Old 04-29-2009, 07:48 AM   #8
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talk to andy at metric, he does porting, and he's into motards
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Old 04-29-2009, 07:57 AM   #9
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Quote:
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That dyno graph is interesting.
That's not a dyno sheet from a KTM single, of course.
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Old 04-29-2009, 08:11 AM   #10
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Quote:
Originally Posted by RACER X View Post
talk to andy at metric, he does porting, and he's into motards
+1 If you're going to allow someone to port the head of that SMR then you better make sure they know what they're doing!!!

Are there any high compression pistons available for you bike Greg? maybe even throw in a cam?
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Old 04-29-2009, 09:03 AM   #11
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Quote:
Originally Posted by RACER X View Post
talk to andy at metric, he does porting, and he's into motards
+1


I would doubt a 5hp gain though.... A busa gains about 8-10hp with a GOOD port job, thats on say a 175rwhp setup... I couldn't see a 5hp gain on a 50rwhp setup....

Maybe though....

Your best bet for a good power gain all across the power band is a big bore kit with higher compression. They probably also make a cam for it to give you some more top end punch....but that can hurt it down low. There is definetly stuff you can do to wake em up, just be prepared to spend the $$$.
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Old 04-29-2009, 09:06 AM   #12
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No replacement for displacement(N/A anyways).

Thought you had a 550 also, Greg.
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Old 04-29-2009, 09:11 AM   #13
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No replacement for displacement(N/A anyways).

Thought you had a 550 also, Greg.
He has a 450 and a 560.
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Old 04-29-2009, 10:57 AM   #14
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^ ya i have both

i love the grunt of the 560 , but love how fast the 450 revs
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Old 04-29-2009, 11:18 AM   #15
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Greg i got your pm.
All his comments and remarks are for the most correct. All in all what you are trying to acheive is velocity of the intake charge into the combustion chamber and the excavation of the burned gases. A higher compression piston can aid in this process because it pushes the gas's out faster but accually doesnt draw in the fuel as fast. That's were making the intake smaller creates more velocity in the venturi to charge the cylinder. You can acheive this with restrictors in the carb at the intake valve side of the carb. Also velocity stacks help with this. Thats why they are called velocity stacks. This is what many manufactures have done over the years. They go to a smaller carb to get velocity. This is really nothing new or ground breaking. He is doing what has already been done. Not knocking him . He is shedding the light on the subject where most can understand the process. But the main thing is. Everything has to jive!! Compression, jetting, cam duration,cam timing, ignition timing.. Any of the above not correct can cause loss HP.......
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Old 04-29-2009, 12:20 PM   #16
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My $0.02. Higher velocities with the same mass flow rate will cause a larger pressure drop per distance (read power loss). What this porting work may do is to "tune" the intake to the engine in a given RPM. Basically the intake air acts like a spring. When the intake valve opens the piston sucks the air and "stretches" the spring. When the valve closes the spring compresses and backs up on top of the valve. At some point there is a peak in the pressure at the valve and if the valve stays closed the air will actually flow backwards. If you can time the opening of the valve to correspond to this pressure peak you will get more air into the piston bore. More air/fuel = more power.
This looks similar to shortening the intake to increase the power at a higher RPM. Wouldn't expect to see power increase in the whole band but rather an elevation at higher RPMs. Unless this is a good porting job that removes the burrs, aligns bores and smooths out any sharp edges that intrude into the flow path. Since this bike is mass produced there are trade offs in tolerances that can lead to these flow restrictions. By removing these the air can flow more quickly into the piston bore which will help the power over the entire RPM range.
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